GM mozzies bred to fight malaria
22 March 2007
Malaria has a new enemy - a GM mosquito that can't carry the killer disease. The new breed can out-compete its wild, disease-carrying cousins too, so scientists hope that releasing swarms of the insect could make mozzie bites harmless instead of deadly.
Antenna finds out what the buzz is about...
Image: CDC/James Gathany, Dr. Frank Collins, University of Notre Dame
Malaria is a deadly blood disease caused by parasites. It's carried from person to person by blood-sucking mosquitoes. Nearly half the world's population are at risk from this tropical disease and over a million people die from it every year.
At the moment, we can only fight the spread of malaria by taking antimalarial drugs and using insecticides against mosquitoes. But neither of these treatments is very effective.
Malaria is most common in Africa, where it kills one child every 30 seconds.
Now American scientists have found another way to combat malaria. They've created a new breed of mosquito that doesn't pick up malaria parasites and can't infect people with malaria when it bites.
'We changed the mosquitoes' genes so that when they drink infected blood, malaria parasites can't break through their stomach to infect them,' explains mosquito breeder Jason Rasgon. 'Instead the parasites are killed as the mosquitoes digest their meal.'
Jason Rasgon, malaria researcher, Johns Hopkins University, USA.
Image: Jason Rasgon
Even more impressively, Jason's team discovered that their malaria-resistant mosquitoes were healthier than wild mosquitoes when fed on a diet of malaria-infected blood. The resistant mozzies lived longer and produced more offspring.
'We combined equal numbers of genetically modified and wild mosquitoes and let them feed on malaria-infected mice,' says Jason. 'After nine generations nearly three-quarters of the mosquitoes were the malaria-resistant type.'
Jason's team studied more than 50,000 caged mosquitoes over the course of a year.
Image: CDC/James Stewart
This is the first time that researchers have been able to create genetically modified mosquitoes that are stronger than wild ones. Before now, scientists thought GM breeds would always be weaker than natural mozzies.
The team's findings could lead to malaria-resistant mosquitoes being released into the wild. They hope eventually to create mosquitoes that can survive and thrive in natural conditions, banishing malaria altogether.
The malaria-resistant mosquitoes were stronger because they didn't have to fight off malaria parasites like these.
Image: CDC/Steven Glenn, Laboratory & Consultation Division
But there's a long way to go before we see GM mozzies in the wild. A new breed would have to be fitter than wild mosquitoes even when they're not exposed to malaria parasites. Researchers haven't achieved this yet.
'We found no difference between our mosquitoes and wild ones when we fed them on malaria-free blood,' says Jason. 'So in the wild, where malaria infection in mosquitoes is rarer, this advantage may not be enough.'
The researchers gave their GM mosquitoes glow-in-the-dark eyes to tell them apart from wild ones.
Image: Marcelo Jacobs-Lorena
Scientists still don't know how to mix genetically modified mosquitoes with wild populations safely and effectively.
'There are lots of ethical issues and regulations to consider before we can introduce new mosquito breeds into the wild,' says Ron Behrens from the London School of Hygiene and Tropical Medicine. 'First we need to consider possible impacts on the environment.'
Ron Behrens, tropical-disease doctor, London School of Hygiene and Tropical Medicine.
Image: Ron Behrens
Jason's team are realistic about the challenges they face. 'Getting our new breed to spread in the wild will be hard,' says Jason. 'I think it will be 10 to 20 years before we can start thinking about releasing them.'
'First we need to start studying these mosquitoes in more realistic environments. We also need to test their ability to control malaria. It's possible that malaria parasites will evolve to infect these mosquitoes too.'
A mosquito's natural habitat is a warm wetland - very different from a science lab.
Image: CDC
But Ron Behrens is confident that this is a big step forward in the fight against malaria. 'This research is an unusual but very exciting approach to malaria control. It shows that malaria can be attacked in several different ways. The best way to beat malaria is with a combination of tactics.'